A CO2 laser or an yttrium-aluminum-garnet (YAG) laser has been mainly used in the field of machining exemplified by welding, cutting, or marking of metal. However, in recent years, a semiconductor laser excited solid-state laser or a semiconductor laser excited fiber laser produces an increasingly higher output power. Thus, in the field of machining described above, the use of semiconductor laser excited solid-state lasers and semiconductor laser excited fiber lasers are increasing in place of CO2 lasers and YAG lasers.
A laser diode is used for a semiconductor laser excited laser oscillation source. To produce a high output power, a laser machine is typically configured such that multiple laser diodes are coupled together in series, in parallel, or in series-parallel to form a laser diode array and thus to cause all the multiple laser diodes to emit light simultaneously. Such a laser diode array requires a large drive current.
In addition, a laser diode is a current-driven element. Therefore, as the power supply device for supplying electrical power to the laser diodes, a high-efficiency, constant-current power supply device is utilized that uses a technique of switched-mode power supply and can supply, at a constant level, a drive current needed for the laser diodes to generate laser oscillation at a desired output power.
It is generally preferable that when a load is a current-driven element, a constant-current power supply device includes, on an output line, an element for storing electromagnetic energy to reduce fluctuations in the current supplied to the load. A reactor is used as such an element for storing electromagnetic energy.
However, since a constant-current power supply device includes a reactor that stores electromagnetic energy, the output current changes more slowly than the current command value changes. In particular, when the current command value is changed from a higher value to a lower value, the constant-current power supply device reduces the output current slowly due to the electromagnetic energy stored in the reactor.
Thus, when the current command value is changed from a higher value to a lower value, a drive current greater than the current command value flows into the laser diodes, thereby preventing the constant-current power supply device from performing suitable machining.
Patent Literature 1 describes a lighting circuit that includes a drive circuit that performs DC/DC conversion on a direct current (DC) supply voltage to obtain an output voltage and supplies an output current that depends on a lighting control signal to one or multiple light-emitting elements; and a forced attenuation circuit connected in parallel to the one or multiple light-emitting elements to forcibly attenuate the output current from the drive circuit in synchronization with the lighting control signal while the one or multiple light-emitting elements are unlit (paragraph [0009]).
Patent Literature 2 describes a light emitting diode (LED) lighting device that includes an LED circuit that includes one or more LEDs; a switched-mode power supply for supplying power to the LED circuit; and a lighting control circuit that drives the switched-mode power supply at a predetermined dimming duty cycle to control lighting of the one or more LEDs, wherein when the lighting control circuit does not drive the switched-mode power supply at the dimming duty cycle, the lighting control circuit drives the switched-mode power supply at a pre-duty cycle that is predetermined (paragraph [0008]).